A. Field of the Invention
This invention relates to separating methods, and more particularly to an electromechanical method for separating clods and the like from potatoes.
B. Description of the Prior Art
In the process of mechanically harvesting potatoes, considerable numbers of clods are excavated therewith. The prior art has attempted to separate these clods from potatoes by various means, including specific gravity differences, form and shape differences, rolling differences, and electro-magnetic differences. For example, in U.S. Pat. No. 2,467,773 sorting was attempted by using the difference in ohmic conductivity of clods and potatoes by piercing the peels of the potatoes with needles, knives, or the like, which causes subsequent premature rotting of the potatoes.
A number of methods have been proposed whereby the potatoes and clods must be transported one by one in single file fashion for detection and subsequent ejection. In some of these proposals it was still necessary to make electric contact with the potatoes and clods, for example U.S. Pat. No. 3,578,160, which is mechanically difficult and which can cause bruising or piercing of the potato and subsequent rotting. A newly harvested potato is quite often covered with a layer of dirt or soil of substantially the same chemical composition as the clods. Thus any mechanical device that must penetrate the soil layer to make electrical contact with the potato may bruise the potato or penetrate the skin or peel of the potato, causing the potato to rot. Penetrating the skin of the potato not only can cause it to rot but can give spurious or false signals from a device which is designed or intended only to make electrical contact with the skin. This occurs because the interior of the potato is of comparatively low ohmic conductivity. Clods vary quite markedly in their ohmic conductivity depending on the chemical composition of the clod and its water content.
Among the proposals to marshal and transport potatoes one by one in a single file are those disclosed in U.S. Pat. Nos. 3,200,888 and 3,268,073. After such marshaling and transporting single file, the objects are dropped one by one through a tube containing a sensing ring which has an oscillator driving such ring. A comparatively electrically conductive object such as a potato reduces the amplitude of the oscillations of the coil as compared to the amplitude of the oscillations when no object or an object of comparatively low conductivity such as a stone or clod is dropped through the sensing coil or ring. The reduced amplitude of the coil oscillating frequency allows detection of a potato and subsequently through magnetic clutches, brakes, and kicker plate mechanisms to advance the potato while rejecting stones, clods and the like.
Making potatoes and clods move in a single file, one by one, is inherently mechanically difficult and expensive. In addition, dropping potatoes any significant distance can subject them to bruising, even if cushioning devices are used. Magnetic brakes, clutches, and kicker plates are inherently slow-acting devices allowing only a relatively slow separation of objects in each file or singulated channel or passageway. This causes a comparatively large machine to be required with a large number of single-file rows with attendant complexity and expense to handle a high volume of potatoes and clods and separate them efficiently. Because of the highly variable nature of a clod's conductivity, depending on its chemical composition and water content, it is common for a detecting device that depends solely on conductivity differences to give spurious responses and rejections when a clod's conductivity approaches that of a potato.
Because the prior art has failed to provide reliable, relatively simple, and economical means to separate clods and potatoes, manual means of separation are still today the state of the art with many workers busily engaged in rejecting clods from potatoes.